1. Field of the Invention
The present invention is directed to a method and apparatus for constraining an edge of a signature in a printing press. In particular, the present invention is directed to a method and apparatus which prevents dog-earring in the open edge of folded signatures which are created in a printing press apparatus, as the folded signatures are transferred between components in the printing press.
2. Description of the Prior Art
In printing presses which print on a continuous web of material, such as, for example, an offset printing press, it is known to cut the printed web into signatures and thereafter to fold the signatures into what are sometimes called books. A signature is a cut section of a web of material in a printing press, whereas a book is a signature that has been folded in one or more places. FIG. 6 is a representation of a signature S which has been folded into a book, and which has a closed or folded edge F and open edges O. Folded signatures S in the form of books are collated and bound together to form a printed product, such as a magazine.
In modern printing presses, it is necessary to cut the web into signatures and fold the signatures into books at very high rates of speed. Alternatively, the web can be folded first, and then the folded web cut into books. Various mechanisms are known for accurately cutting a printed web into signatures of relatively uniform size, and thereafter folding the signatures into books of relatively uniform size, all at high rates of speed. Various mechanisms are also known for folding a web, and thereafter accurately cutting the printed and folded web into books of relatively uniform size, also at high rates of speed.
In known printing press apparatuses, folded signatures in the form of books emerge from cutting and folding mechanisms via a tape drive. FIG. 4 is a side, cross-sectional view, and FIG. 5 a partial perspective view, of a prior art printing press in which a folded signature S emerges in a direction D from a cutting and folding mechanism M via a tape drive T The tape drive T includes one or more tapes or belts B, moving continuously in a direction d, which engage at least one side of the folded signature or book S and conveys it in a linear direction. Usually, the tape drive T will include a tape or belt B which overlaps the open edges O of the folded signature or book S and is of sufficient width so that variations in the folded width W of the folded signature or book S will result in the open edges O always projecting under the tape or belt B. That arrangement therefore ensures that the open edges O are held down by the tape or belt B, preventing dog-earring of the corners C of the open edges O.
The tape drive T in the prior art apparatus of FIG. 4 transfers the folded signature or book S to transfer device 101. The transfer device 101 may rotate in a direction R1, and include some mechanism to secure a folded signature or book S to its outer surface. The signature S shown in FIG. 4 is transferred by tape drive T to the outer circumference of the transfer device 101, and after traversing a gap G in an unconstrained manner, the leading edge l of signature S is gripped by a leading edge gripping mechanism 4, 5 which projects from the periphery of a deceleration drum 6 (the periphery of which is indicated in dashed lines) rotating in a direction R2.
One problem with the known folded signature or book transfer mechanism as shown in FIGS. 4 and 5 is that the comers C of the open edge O of the folded signatures or books S have a tendency to dog-ear during transfer from the tape drive T to the deceleration drum 6, from the tape drive T to the transfer device 101, or from the transfer device 101 to any other transfer mechanism, such as a downstream deceleration drum. Dog-earring is a condition where a corner Cxe2x80x2 or edge of a flexible sheet or signature bends or folds over in an undesirable manner, as shown in dashed lines in FIG. 6. One solution which has been used to reduce the occurrence of dog-earring of the folded signatures or books S during the transfer steps is to electrostatically charge the folded signatures or books S. In one prior art arrangement, the web passes over a folder and is folded in one or more places. The folded web is then electrostatically charged by producing a voltage across the folded web, and then the charged web is cut into folded signatures or books S. As a result, the charge on the folded signature or book S results in the sides of the folded signature or book S being electrostatically attracted, and adhered, to one another. This adhering of the two charged sides results in the open edges O adhering to one another, thereby increasing the thickness of the open edge O presented to the transfer mechanisms, and reducing the chance that a corner will be unrestrained and become dog-eared.
A disadvantage which has been discovered in the known use of electrostatic adherence to prevent dog-earring is that the electrostatic adherence can become a hindrance to subsequent operations on the folded signature or book S. For example, if it is desired to collate a series of folded signatures or books S by interleaving the folded signatures or books S to form a magazine, the open edges O of a folded signature or book S must be opened relative to one another to allow another folded signature or book to be inserted between them. However, the electrostatic adherence of the open edges O to one another hinders both the opening, and the interleaving, operations. Another problem with the use of electrostatic adherence is that it is not a positive control of the open edge O of the folded signature or book S, and therefore dog-earring can still occur despite the increased stiffness of the open edge O caused by the electrostatic adherence.
The present invention is an apparatus and method designed to eliminate dog-earring of the corners C of the open edges of a folded signature or book S without the need for the use of electrostatic adherence. The apparatus and method of the present invention, therefore, provides advantages over known transfer techniques because it does not present a potential hindrance to subsequent operations of the folded signatures or books S.
In the apparatus of the present invention, a guide mechanism is provided between, for example, a tape drive, a divert cylinder and/or a deceleration drum. The guide mechanism is preferably located at the position of the open edges of the signature which is being transferred, although additional guide mechanisms could be located in other positions as well. The guide mechanism is preferably of a width which accommodates variations in the folded width of the folded signature or books. The guide mechanism includes a series of narrow slots, or micro-slots, across its width. The gripping devices which are located in the area of the guide mechanism include a series of narrow fingers, or micro-fingers, across their width. The micro-fingers of the gripping mechanisms are designed to pass through the micro-slots of the guide mechanism. The guide mechanism is designed to constrain movement of the open edge of the folded signature away from the transfer mechanism across any gap between transfer mechanisms, thereby preventing dog-earring of the open edges of the folded signatures or books as they are transferred between transfer mechanisms.
In the method of the present invention, folded signatures or books are transferred between a transfer mechanism and a guide mechanism which is located at least in the area of the open edges of the folded signature or book. The guide mechanism include a series of narrow slots or micro-slots across its width, each of which extend along the length of the guide mechanism. A transfer gripper, including a series of narrow fingers or micro-fingers, is used to grip the folded signature or book before it emerges from an end of the guide mechanism. The micro-fingers of the transfer mechanism pass through the micro-slots in the guide mechanism to thereby allow the folded signature or book to be gripped before it emerges from the end of the guide mechanism.